States. Approximately 2.5 million chlamydial infections occur in women each year, resulting in pelvic inflammatory disease, ectopic pregnancy, and infertility. Health care costs attributed to chlamydial infections and their sequelae reached $4.2 billion in 1990. Given the prevalence, reproductive consequences, treatment limitations, and economic impact of C. trachomatis and other sexually transmitted infections worldwide, the potential role of topical microbicides in preventing infection must be examined. The major objective of the proposed studies is to investigate the effectiveness of currently available (or newly developed) topical microbicides in preventing or controlling the transmission of cervical chlamydial infection in vivo. We plan to utilize the female pig-tailed macaque animal model for two reasons. First the vaginal flora of the pig- tailed macaque is very similar to humans; second, the model provides a predictable, highly reproducible model for C. trachomatis cervical infection. The specific aims are: 1) characterize the effects of topical microbicides on the microbiology of the vaginal ecosystem without chlamydia; 2) evaluate the effects of intravaginal microbicides on C. trachomatis infection in the pig-tailed macaque model; 3) characterize the cytopathologic and immunologic reactions of the vaginal and cervical tissue in response to exposure to topical microbicides in the presence or absence of chlamydial infection; and 4) characterize the host/pathogen interactions during the early stages of C. trachomatis cervical infection to determine 'whether application of the microbicide prior to sexual contact is necessary to prevent chlamydial infection. These studies will provide information critical to the design of clinical trials of topical microbicides for protection against transmission of sexually transmitted diseases.